We will continue to investigate the biochemical and physiological properties of freshly isolated retinal microvessels, and of their constituent cells grown in culture. Specific topics of investigation will include: (a) The macromolecular components of the microvascular basement membrane obtained from intact vessels isolated from fresh tissue and also synthesized by retinal capillary cells in culture. These include collagens and proteoglycans, and noncollagenous proteins such as laminin and fibronectin. The effect on the synthesis of these macromolecules of elevated levels of glucose, galactose, and xylose, and of the aldose reductase inhibitor Sorbinil will be studied. (b) The properties of receptors on the cell membranes of retinal vascular cells for hormones that induce smooth muscle contraction or relaxation; these include Alpha- and beta-adrenergic agents and angiotensin II. The purpose of this investigation is to determine, first, if pericytes are contractile cells analogous to the smooth muscle cells of larger vessels; second, if there are differences in the behavior of pericytes and endothelial cells to these agents, and third, whether the response of retinal vascular cells to these hormones is altered in the presence of elevated concentrations of glucose or other sugars, or in the presence of any of these sugars together with an aldose reductase inhibitor. (c) We will investigate, by transmission electron microscopy, the morphological differentiation of retinal capillary cells in culture, paying particular attention to the development of such features as intercellular junctions, as well as to the appearance of apparent vascular "lumina". Additional morphologic studies will include localization of a fluorescein labeled lectin probe (Ulex europaeus I lectin) as a marker for cultured capillary endothelium and morphometric analyses of scanning electron micrographs of cultured capillary endothelial cells incubated with platelets as a measure of platelet adhesiveness under normal, high glucose and high galactose culture conditions. The overall aims of this research are to understand better how this normal physiology may be altered by conditions simulating diabetes mellitus.